- #1
brushman
- 113
- 1
Homework Statement
Look for a matrix that has row sums 4 and 8, and column sums 2 and x:
matrix =
[a, b] -------I don't know how to do latex
[c, d]
a + b = 4; a + c = 2;
c + d = 8; b + d = s;
The four equations are solvable only if s = ____. Then find two different matrices that have the correct row and column sums. Write down the 4 by 4 system Ax = b with x = (a, b, c, d) and make A triangular by elimination.
Attempt at a solution:
I created a matrix from the system of equations given. I started with:
[1 1 0 0 4]
[0 0 1 1 8]
[1 0 1 0 2]
[0 1 0 1 s]
-->[1 1 0 0 4]
[0 -1 1 0 -2]
[0 0 1 1 8]
[0 0 1 1 (s-2)]
-->
[1 1 0 0 4]
[0 -1 1 0 -2]
[0 0 1 1 8]
[0 0 0 0 (s-10)]
So I got s = 10.
I can't solve for a, b, c, or d (or can I?)
What am I not understanding and how do I do this problem? Thanks.
edit: Thanks LCKurtz, I got it now.
Look for a matrix that has row sums 4 and 8, and column sums 2 and x:
matrix =
[a, b] -------I don't know how to do latex
[c, d]
a + b = 4; a + c = 2;
c + d = 8; b + d = s;
The four equations are solvable only if s = ____. Then find two different matrices that have the correct row and column sums. Write down the 4 by 4 system Ax = b with x = (a, b, c, d) and make A triangular by elimination.
Attempt at a solution:
I created a matrix from the system of equations given. I started with:
[1 1 0 0 4]
[0 0 1 1 8]
[1 0 1 0 2]
[0 1 0 1 s]
-->[1 1 0 0 4]
[0 -1 1 0 -2]
[0 0 1 1 8]
[0 0 1 1 (s-2)]
-->
[1 1 0 0 4]
[0 -1 1 0 -2]
[0 0 1 1 8]
[0 0 0 0 (s-10)]
So I got s = 10.
I can't solve for a, b, c, or d (or can I?)
What am I not understanding and how do I do this problem? Thanks.
edit: Thanks LCKurtz, I got it now.
Last edited: